Spicing Things Up
Of course, for that first question, simulation may offer a worthy alternative to hands-on measurements. Here, I reproduced the SA-1810's circuitry in LTSpice with some help from Harford's patents to fill in blanks. Robert from ESP kindly providedparameters for the EMI filter magnetics and actual waveforms so I could sanity check my simulation model against them.
Vin is the input voltage with a standard B-class (1.2x50/8x20) surge applied to it, I(V300) is the current passing through the simulated source and finally, Vout(P-N) is the voltage across output live and neutral. After the EMI filter, there is effectively nothing left of the surge and the output voltage peaks at a completely benign 184V, merely 14V above nominal for 120VAC.
What is the lazy hump after the initial surge? Simply the shunt capacitors (C4/C6) finishing to charge since normal SCRs cannot turn off until their anode current drops near zero.
For Comparison's Sake
Since I went through the trouble of modeling a combination wave surge generator, I thought I may as well pick up a MOV spice model (Epcos S20K130 here), whack it in and see what happens. After much fiddling with circuit and spice parameters to get around “time step too small” errors, I managed to get these waveforms.
As before, Vin is the input, Ix is the current through the MOV and Vmov is the voltage across the MOV, which also counts as the output voltage. The MOV peaks at 420V and 1700A, 250V above peak AC voltage.
Why don't the voltage input and current waveforms peak at 6kV and 3kA? The first reason is because the specifications are 6kV 1.2x50µs open-circuit and 3kA 8/20µs short-circuit, so the two conditions are intrinsically mutually exclusive since you cannot have 6kV across a short-circuit. The second is that as-modeled, my combination wave pulse shaper only went up to 4.5kV/2.5kA, so not quite up to full spec.
Wrapping Up
If you were starting to grow tired of power strips that all seemed to look mostly the same inside, the SA-1810 is definitely something different. Through clever use of magnetics, semiconductors and large capacitors, it achieves power line surge suppression that MOVs cannot match. Even after tweaking my surge generator model some more to get closer to 6kV/3kA, the peak output remained under 200V, well within even the most sensitive electronics' comfort zone.
I really liked the overall construction except for the use of RTV to secure the reactor instead of nuts, in equal parts because the RTV failed in my unit and if it had stuck, I would have had to pry it off for the tear-down. This would have likely involved mangling the reactor's sticker, scratching the reactor housing and bottom tray.
Despite its great surge elimination performance and build quality, I cannot help feeling like the $400 street price is still too steep for what it is and does. If you have a large collection of sensitive electronics to protect, though, it should be worth considering.
Thanks go to Nicholas from Caster Communications for having the unit shipped to me, Robert from ESP for sharing his engineering insight, and readers like you whose on-going interest in these stories drive the manufacturers' interest in participating.
